Wretling M L, Henriksson-Larsén K, Gerdle B
Department of Clinical Physiology, University of Umeå, Sweden.
Eur J Appl Physiol Occup Physiol. 1997;76(6):483-90. doi: 10.1007/s004210050279.
Changes in mechanical performance and electromyographic activity during fatiguing dynamic knee-extensions were evaluated with respect to muscle fibre type composition of the vastus lateralis muscle in nine sedentary female [23 (3) years] volunteers. The subjects performed 150 repetitive maximum knee-extensions using a Cybex dynamometer at 1.57 rad x s(-1). EMG activity was recorded from the vastus lateralis, the vastus medialis and the rectus femoris muscles. For each contraction, mean power frequency (MPF) and the root mean square (RMS) of the EMG were calculated, simultaneously with the peak torque (PT), contractional work (CW) and the mean power (MP). The MPF showed an initial decrease followed by a stable phase. The RMS increased during the initial seven contractions, after which a period of variability was displayed until about the 60th contraction. At the plateau level (last 50 contractions) the relative RMS values were not significantly different from the initial values. The PT, CW and MP increased during the initial five to ten contractions, after which a two-phase pattern was displayed, with a gradual decline followed by a stable phase. The absolute plateau level of MPF for the vastus lateralis muscle showed a significant negative correlation with the area percentage of type-1 fibres (r = -0.71). Significant correlations were also demonstrated to occur between the absolute plateau levels of PT, CW and MP and the relative proportion of type-1 fibres (r = 0.80, r = 0.82 and r = 0.82 respectively). Thus, in female subjects the mechanical performance and the MPF during fatigue are at least partly determined by muscle morphology.
针对9名久坐不动的女性[23（3）岁]志愿者，研究了股外侧肌的肌纤维类型组成与疲劳性动态伸膝过程中力学性能和肌电图活动变化之间的关系。受试者使用Cybex测力计以1.57弧度×秒⁻¹的速度进行150次重复性最大伸膝动作。记录股外侧肌、股内侧肌和股直肌的肌电图活动。对于每次收缩，计算肌电图的平均功率频率（MPF）和均方根（RMS），同时记录峰值扭矩（PT）、收缩功（CW）和平均功率（MP）。MPF最初下降，随后进入稳定阶段。RMS在最初7次收缩期间增加，之后呈现一段波动期，直到约第60次收缩。在平台期（最后50次收缩），相对RMS值与初始值无显著差异。PT、CW和MP在最初5至10次收缩期间增加，之后呈现两阶段模式，先是逐渐下降，然后进入稳定阶段。股外侧肌MPF的绝对平台期水平与I型纤维的面积百分比呈显著负相关（r = -0.71）。PT、CW和MP的绝对平台期水平与I型纤维的相对比例之间也显示出显著相关性（分别为r = 0.80、r = 0.82和r = 0.82）。因此，在女性受试者中，疲劳期间的力学性能和MPF至少部分由肌肉形态决定。
